The present invention relates to conveyor systems and in particular to a vertically self-centering, belt driven conveyor system for surfacing machinery such as rough lumber abrasive planers utilizing endless abrasive belts, and wherein the system is adapted to remove substantially equal quantities of material from both sides of the lumber being treated without damaging, marring, scratching or otherwise generating surface irregularities on the work.
Driven belt conveyor systems have long been used as an infeed for delivering various flat stock to a variety of surface treating machinery including rough lumber being delivered to or passed through an abrasive planer. Such infeed conveyors typically utilize a base belt having one or more pinch wheels mounted thereabove. One or more drive rollers are utilized to drive the conveyor belt and the flat stock such as rough lumber is supported on the belt and held in the zone between the belt and the pinch wheels while moving through the machine. In this fashion, the flat stock is typically indexed relative to the surface of the moving conveyor belt rather than the stock itself and accordingly unequal amounts of materials are normally removed from the two major surfaces of the stock as it moves through the surfacing machinery. Furthermore, such systems assume that each stock element or workpiece being treated has at least one relatively flat surface and that any irregularities in individual incoming workpieces are averaged out over the entire supply. One problem which has frequently developed in conveyor systems which function as a driving means to pass work through any type of surfacing machinery has been the creation of mars, scratches or other imperfections on the surface. The creation of any such surface imperfection is a particularly undesirable result, particularly with wood designed for use as furniture or finishing material. While apparatus for finishing a single surface of material have been widely utilized, such apparatus has a disadvantage of either requiring multiple passes on a single machine, or requiring spaced apart operations on a single such machine. Either type of machine is more costly to operate than the apparatus of the present invention, and any added handling operations tend to increase the likelihood of creation of mars or scratches on the surface of the work being finished.
An example of a piece of single surfacing apparatus for minimizing finish irregularities can be seen upon reference to U.S. Pat. No. 3,694,966. An elastically flexible load beam is disclosed therein which coacts with the endless abrasive belt to vary the pressure applied to the stock being surface finished. In such system, however, the entire work station or surfacing element is moved in response to the sensing of irregularities in the stock. By way of contrast in the present apparatus, the supports for the conveyor flex or shift in response to irregularities in stock thickness so as to maintain the central axis or plane of the stock at a constant vertical elevation, while the supports for the abrasive machinery which determine the working plane of the abrasive belts normally remain stationary.
Two shortcomings of prior systems however are that while such dimensional averaging techniques may apply for most pieces of stock, they do not apply in all cases, and it is the unusual occurrence which tends to create problems in the finished product. For example, due to the randomness of occurrences of irregularities in the incoming stock, waves or cusp patterns may be generated in the finished surfaces. Also, one sided surfacing machines require more finishing time, in that multiple passes are required in order to reduce the stock to its ultimate finished thickness.
The present invention is concerned with surfacing equipment that simultaneously finishes the upper and lower surfaces of rough stock, without requiring periodic movement or adjustment of the surfacing assemblies, with the equipment being adapted to remove substantially equal amounts of excess material from both surfaces of the stock. Consequently, the apparatus of the present invention employs two stationary endless abrasive belt sanders and a novel feedworks that vertically and laterally centers the incoming unfinished stock relative to the working surfaces of the endless abrasive belts. Details as to the construction of typical endless abrasive belt sanding apparatus which are adapted for use with the present invention can be found upon reference to U.S. Pat. No. 4,594,815, or U.S. Pat. No. 4,187,645 (both of which are assigned to the present assignee).
In accordance with the present invention, proper stock alignment for incoming workpieces is achieved via a vertically floating feedworks assembly, whereby irregularities in the thickness of the incoming workpieces are accommodated by the simultaneous flexural response of both upper and lower pinch and drive rollers. Therefore, irregularities in thickness of incoming stock are sensed and accommodated without vertically varying the elevation of the central plane of the individual workpieces as they are fed in and through the surfacing apparatus. The inventon employs a lower workpiece supporting conveyor belt which is held in contact with the incoming workpieces by a plurality of individual pivotally mounted floating support wheels associated with the drive assembly. These individual floating support wheels are spaced apart from one another both longitudinally and transversely, and otherwise arranged in a staggered relationship and are pivotally mounted on the base frame so as to permit deflection or flexure upon detecting or sensing surface irregularities along the underside of the incoming workpiece, with the deflection or flexural response of the floating support wheels permitting uninterrupted feed of the unfinished stock. This uninterrupted incoming feed is accomplished without varying the central plane of the individual incoming workpieces. Lateral or side movement is also minimized due to the forgiving but firm gripping action of the pivotally mounted support wheels, with a relatively constant pressure being thereby maintained across the width of the stock.
The apparatus of the present invention employs a lower work supporting drive means, such as a reinforced rubber conveyor belt along with a cooperating upper hold-down means such as a second plurality of individual pivotally mounted floating support wheels, with the combination neither marking nor marring the lumber stock or work as it is moved through the working stations of the machine. The arrangement is such that the incoming feed exerts a constant force on the incoming work. Such treatment of the work reduces the danger of marring or marking the surface of the lumber, and at the same time advantageously permits clean-up operations to be performed on lumber of scant or slight thickness dimensions. Such advantages are not available from other known types of mechanical feeds, and are particularly unavailable from those which have been found to create surface defects when irregular work is passed therethrough.
It is therefore a primary object of the present invention to provide an incoming feed assembly for drivably supporting workpieces on its upper and lower surfaces in a floating fashion.
It is another object to provide an assembly having upper and lower sets of individually mounted floating support wheels, with the lower set including a plurality of floating support wheels for maintaining a portion of the flight or span of a work supporting conveyor belt at a desired elevation, with the overall assembly being designed to deliver work stock into a surface treating station under a substantially constant force.
It is a further object to provide a mounting arrangement for floating work supporting wheels in a spaced apart and laterally staggered relationship such that each successive wheel encounters various different surface areas of the workpieces moving therethrough.
It is a still further object of the present invention to provide for means to independently and pivotally mount each of the individual floating support wheels in mutually adjacent staggered relationship, one for another, so as to minimize or prevent axial movement or wandering of the incoming workpieces.
The above objects and advantages, as well as others, will however become more apparent upon reference to the following description with respect to the following drawings.